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Why Thermal Energy Storage?

Sudhakar Neti Senior Research Scientist Energy Research Center,

Lehigh University Bethlehem, PA 18015 USA

All our life and energy come from our Sun 2

Unlike many newly discovered Exoplanets Our Earth is a ‘Goldie

Locks’ planet

All our life and energy come from our Sun

Every hour, the sun

radiates more energy

onto the earth than the

entire human population

uses in

one whole year.

Abundance of Energy

Total U.S. Electricity

Generation Capacity in 2013 = ~1 TW

At 80% solar

collection h & 30%

plant h,

65 km x 65 km will

generate all the U.S.

Capacity

http://www.eia.doe.gov/ 4

Think of the area allocated to a Hydroelectric dam – 25 to 100 sq. km.

All our life and energy come from our Sun

• Renewable energies are intermittent and do not match load patterns

• Wind electricity usually is at night – load factor ~30%

• PV or CPV generate electricity

• Storage of electricity is still in its infancy ! o Li-ion Batteries (250 Wh/kg, gasoline ~ 12,000

Wh/kg), Super Capacitors, limited to MWh

o Pumped Hydro, Compressed Air, H2 and CH4

and Organic Quinones for flow batteries M. Aziz (50 mW cm-2)

Need for Energy Storage Technologies

Solar Thermal Energy (CSP)

6 From: DOE 2013 Workshop – Ranga Pitchumani

Choices of Solar Technologies

2007, 11MWe

Solar power

tower in Spain

Cost of $47.8m

($4.35/We).

624 heliostats,

120m2 each;

150 acres

Point Concentrator with Cavity Receiver

• 7.5 m dia, 42 m2 area • Monococque Design with

Al Reflectror • 2-axis tracking • 30 kWth

• Compete with fossil fuels $/W

CSP Worldwide

9 From: DOE 2013 Workshop – Ranga Pitchumani

All our life and energy come from our Sun

• Essential for CSP

• Important also for Buildings

• Industrial applications

• Military applications • Directed energy weapons

• Expendable media vs. reuse of materials

• Regenerative condensed-phase TES: 0.5 MJ/kg, 500 MJ/m3, 2 kW/kg High energy-density expendable TES: 1–2 MJ/kg, 1,000–2,000 MJ/m3, 5 kW/k

Soumya Patnaik – AFRL – Dayton, OH

Thermal Energy Storage Technologies

All our life and energy come from our Sun

• Low Temp Applications - < 90oC

• HVAC ~ 50-120oC

• Desalination ~ 90-100oC

• Process Heat - > 200oC

• Power Generation - >350oC

• Combined Heat and Power -- CHP

Uses of Solar Thermal Energy

All our life and energy come from our Sun

Energy Storage Technologies for CSP

• Storage as Hydrogen (Solar catalysis H2)

• Storage of high pressure water

• Storage of sensible heat – salts, sand, etc.

• Storage as latent heat

• Organic Media (< 200oC)

• Inorganic Salts

• Salt Eutectics

• Molten metals

• Metal Oxides

Thermal Energy Storage Schematic

Thermal Energy can be stored directly in hundreds of MWh quantities

Temperature Ranges of Interest – HIGH 500 to 750C, MEDIUM 300C, LOW 29C

Thermal Energy Storage - Methods

Challenges

• Very Capital intensive – but NO fuel costs

• Lack of Capital – Risk vs. Bankability

• Technology growth – still in research stage !

• Maturity of Industry – poor choices made

• Improve efficiency – collection and conversion

• Shortage of materials – NaNO3 price increases??

• Cost mitigation to meet Solar < Fossil • $4,000/kW $2,000/kW • $0.21/kWh $0.06/kWh

Cost of Solar Thermal Energy (CSP)

2010 – Total $0.21 / kWh & Reductions

Solar field $0.09 - $0.07

Power plant $0.04 - $0.02

Receiver/HT $0.03 - $0.02

Thermal Storage $0.05 - $0.04

2020 -- Total Target $0.06 /kWh !

17 From: DOE 2013 Workshop – Ranga Pitchumani

Energy and Exergy Analysis

TES Systems Considered • Al • NaCl • MgCl2

• NaCl / MgCl2 • KNO3 • NaNO3 • KNO3/ NaNO3 • NaNO2 • NaNO3/NaNO2 • KNO3/NaNO3/NaNO2 • Sensible heat only

• Convection and Void I EPCM

• Charging and Dicharging Temps (~551 K, ~660 K)

• 12 hr charging & discharging cycles

• 0.26 kg/m2-s mass flux

• LCOE Analysis

Metal Oxides as PCM -- Comparison

Material Tm

(°C)

Latent Heat

(kJ/kg)

Solid Cp

(J/kg K)

Liquid Cp

(J/kg K) Material

Tm

(°C)

Latent Heat

(kJ/kg)

NaNO3 308 162.5 1588 1650 K2B4O7 816 446.4

MgCl­2 714 454 798 974 KBO2 947 383.4

NaCl 800 481 987 1200 Na4P2O7 970 220.4

Al 660 397.3 903 1177 KPO3 810 74.5

Na2B4O7 742 403.5 1174.3 2213.3 K2SiO3 976 325.4

NaBO2 967 509.1 1349.8 2218.8

Na4B­2O5 641 617.3 1166.4 2048.8

Oxides have higher energy densities at comparable melting temperatures

Metal OXIDES

Materials Tested in EPCM for Thermal Energy Storage Capsules

The EPCM capsule void is filled with an inert gas such as Argon.

Photo of sectioned EPCM capsule with NaCl-

MgCl2 eutectic after significant thermal

cycling for temperatures ~500 °C.

Photo of sectioned MgCl2 EPCM capsule

after significant thermal cycling for

temperatures ~750 °C.

NaNO3 Tests – Energy Storage and Retrieval

0 0.5 1 1.5 2 2.5 3 3.50

5

10

15

20

Time (hr)

En

erg

y S

tore

d i

n N

aN

O 3 C

ap

sule

s (M

J)

QNaNO

3

0 0.5 1 1.5 2 2.5 3 3.50

100

200

300

400

Time (hr)

NaN

O3 T

em

pera

ture

(oC

)

NaNO3 Temperature

∆Q ~100°C

Phase change

contributes

37% of ∆ Q ~100°C

~ 100°C

Thermal Storage Technologies for Solar Power SOME NECESSARY RESEARCH STEPS

• Storage Shift Modes – Temporal, Spatial • Storage Technology – Sensible, Latent, Chemical • Choice of PCM & EPCM – Materials for Temperature (29C to 750C) • Preparation of PCM and Determination of properties • Choice of New PCM and Corrosion considerations • Testing of EPCM – Calorimetry, Thermocline Flow Experiments –

Lab and prototype • Numerical prediction of Transient Temperature Distributions • Thermal Energy Storage, Retrieval and Exergy Analysis • Cost - LCOE - analysis for high temperature EPCM with continued

decrease of costs (~<$15/kWhthCapital cost).

Summary • Fossil fuels will be in use for decades

• Energy challenges driven by CO2 and global warming

• Nuclear has its own uncertainties

• Abundance of solar energy – Wind, PV, CSP

• Storage of electricity is still in its infancy !

• Costs of implementation of CSP needs to be brought down

• Challenges – Capital, Bankability! Thermal Energy Storage has great potential

– has broad implications.

Thank you.

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Gracias.

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